The impact forces that must be attenuated by an article of footwear vary considerably between individuals and within individuals depending on the type of activity and the intensity and duration of the activity undertaken by the individual. For example, a large population of individuals sharing the same shoe size such as US Men's size 9 can vary in body mass from 50 kg to over 100 kg. Also that same group of individuals may practice a range of sports or work activities while wearing a give type of shoe, or they may practice these activities at a wide range of intensities. Biomechanical research has shown that the impact forces experienced underfoot are highly dependent on the type and intensity of the activity and on the mass of the individual participant. Therefore an article of footwear produced in a given size may be required to attenuate impact forces as low as a few hundred Newtons of force or as high as several thousand Newtons. Conventional foam materials and other materials used to attenuate impact forces in footwear are not fully functional over such a wide range.
Therefore a shock attenuating technology must either be capable of being precisely engineered to meet the requirements of a particular individual as well as the particular impact forces experienced as a consequence of undertaking a particular activity, or, the technology must be adjustable either passively or actively in response to the load or the expected load. Passively adjusting shock attenuation requires that the system adjust itself without the intervention of the individual. Active adjustment requires that the individual or, some other agent uses some means of adjustment to change the properties of the shock attenuating system.
Therefore, it is needed to produce a shock absorbing system precisely engineered to absorb a specified but limited range of impact shock magnitudes or to create passively or actively adjustable systems that can be adjusted over a wider range. In the case of the fixed system, the shock attenuating properties may be engineered for individuals of a particular range of body masses, or, for certain limited and defined activities.
An adjustable version of such a need may be used to adjust or fine tune the shock attenuating response to match the specific requirements of the individual or activity, or, to accommodate changing shock attenuating demands caused by different environmental conditions.
Therefore, it is needed to provide the following two factors:
1: a shock attenuating technology that can be precisely engineered to produce a wide-range of shock attenuating properties.
2: a shock attenuating technology that is inherently adjustable in terms of its mechanical properties so that it may be used to produce cushioning systems that can be precisely adjusted to provide a wide-range of shock attenuating properties.
An arch is one of the most efficient load bearing structures. It provides relatively greater stiffness for load bearing per mass or thickness than other structures. When the arch is used as a cushioning structure, however, it must be able to flex to provide compliance, a necessary feature of all cushioning systems. However, when an arch is made to be compliant when subjected to a given load it tends to be slow to return to its initial shape, and it is susceptible to buckling. This can be helped by the selection of materials that are resilient and tend to retain their shape, but these materials are also less compliant and therefore less able to provide adequate shock attenuation. By itself the arch is not able to provide all the properties required of a shock attenuating system.
Likewise, resilient elastic materials are good at absorbing and returning energy and deforming under load, but generally they do not have enough structural integrity to provide all the properties required of a shock attenuating system.